Loaded conductor



April 1929- w. s. SMITH ET AL O 1,710,805

LOADED CONDUCTOR Filed May 5, 1928 mam INVENTORS W.S.SMITH, H.JAGARNETT & J-A-HOLDEN By Their Attorneys,

Patented Apr. 30, 1929.

UNITED STATES PATENT OFFICE.

WILLOUGHBY STATHAM SMITH, OF BENCHAMS, HENRY JOSEPH GARNETEIJ, OF LYMNE, .AND JOHN ANGEL 'HOLDEN, 0F SUNNYSIDE, ENGLAND.

LOADED CONDUCTOR.

Application filed May 3, 1928, Serial No. 274,961, and in Great Britain April 30, 1927.

Many alloys are known which have high magnetic permeability in minute fields of force together with high electrical resistance. Such alloys usually contain a large percentage of nickel in conjunction with other elements, and they are in consequence costly to produce, so much so, that in many cases they cannot be used and resource has to be made to a cheaper material, such as ingot iron, Swedish charcoal iron, etc. Further, the high permeability nickel alloys fail in certain applications because their permeability is greater than is required, and in consequence the losses due to added resistance outweigh the advantages secured by the high permeability.

As a result of many researches, we have found that it is possible to produce economically, alloys which have magnetic per-' meability much superior to that of the best Swedish charcoal iron and an electrical resistance from five to eight times as great. These alloys consist-mainly of iron with suitable proportions of chromium and aluminium. They can be made in open hearth furnaces, Bessemer converters, by the crucible process, in are electric furnaces or in induction furnaces.

In order to secure the best results, a very low carbon content is essential and for this reason, where the highest magnetic permeability in fields tending to zero is required, an induction type of furnace is preferred.

According to one feature of this invention an alloy of iron, chromium and aluminium comprising a chromium content of more than 1% but less than an aluminium content of 1% to 4%, and the balance iron is employed in the production of a magnetic material having high permeability.

Alloys made in accordance with a further feature of the invention comprise a chromium content of more than 4% but less than 10%, anlaluminium content of 1% to 4% and the balance iron. Preferably the aluminium content is within the range of 2% to 3.8%. Manganese may be present to assist in obtaining workability but it is not essentlal: silicon may also be present for the same purpose but the content of each or both elements should not exceed 1%. It is possible to obtainalmost equally good results by substituting molybdenum or a suitable combination of chromium and molybdenum for the chrom um, but as molybdenum is more costly there is no advantage in so doing.

To secure workability, particularly in the cold working stages, the alloys should contam a chromium content in excess of the aluminium content.

Unlike those binary iron-chromium alloys rlch in chromium, the alloys described herein are very soft, malleable and ductile, and can be easily reduced to fine wire by the methods well known in the art.

To illustrate the properties of the alloys the following examples are cited.

Four ingots of the undermentioned composition were melted in an induction furnace from charges consisting of Swedish charcoal iron, containing 04% carbon, metallic chromium, pure aluminium. Manganese equal to was added as a casting addition. The resulting ingots were forged, rolled and drawn to wire with annealings as required. Finally, the wires were annealed at 900 C. for 3 minutes; they were tested for permeability in a field of .005 gauss and the electrical resistance was then measured.

No. 1 No. 2 No. 3 No. 4 5% Cr. 5% Cr. 7% Cr. 9% Cr. 1.75% A1. 3.8% A1. 3.8% A1. 2.9% A1. The remainder iron.

No.1 No.2 No.3 No.4

Magnetic permeability with H=.005 435 380 I 380 380 Electrical resistance per cm. 86 100 89 In addition to high electrical resistance and high magnetic permeability, the alloys have hysteresis lower than that of charcoal iron.

To illustrate the application of these alloys to loading telephone conductors, wire from alloy (1) was ,wound upon a copper conductor and heat treated by winding through a tube furnace at 900 C. and cooling in an inert atmosphere, the inductance of the loaded conductor was then found to be equal to a permeability of 385 with a magnetizing force equal to .001 c. g. s. units.

The magnetic permeability of these alloys is influenced by heat treatment, thus No. 1 alloy after heating to 1020 C. and cooling, had an initial permeability of 590 and No. 2 alloy, after the same treatment, had an initial permeability of 460. g

It will be understood therefore that alloys in accordance with this invention may be made into wires, ribbons, etc. orother suitable form for loading telephone conductors which may then be'heat treated so that the loading develops an initial permeability of theorder of 250-400. Theymay also .be

made into any other form suchas tapes,

curve of wire from alloy No. 2, heat treated by heating to 1020 C. and cooling; it

will be noticed that at H of 90, the B is 18,000. I

We are aware that in the manufacture of articles hardened in their marginal layers by nitrogenizat-ion, it has been proposed to make a steel alloy which contains .5 to 2% of aluminium, and, separately, or in any desired combination, silicon, manganese, nickel, chromium, molybdenum, tungsten, vanadium, titanium or zirconium, amounting in all from .5 to 4% and up to .6% of carbon, a specific example of which alloy contains 0.5%-2% of aluminium and 0.5%3% of chromium, but we make no claim to such process.

What we claim is 1 The combination with an electrical conductor, of substantially carbon free loading material applied to said conductor and comprising chromium 4% to 10% of the whole, aluminum 1% to 4% of the whole, and the balance mainly iron.

2. The combination with an electrical conductor, of substantially carbon tree loading material applied to said conductor and comprising chromium 5% to 9% of the whole, aluminum 1.75% to 3.8% of the whole, and the balance mainly iron.

3. The combination with an electrical conductor, of substantially carbon free loading material applied to said conductor and comprising chromium 4% to 10% of the whole, aluminum 1% to 4% of the whole, and the balance mainly iron, said material having had the desired magnetic properties developed by annealing at or above 900 C.

4. The combination with an electrical conductor, of substantially carbon free loading material applied to said conductor and comprisingchromium 4% to 10% of the whole, aluminum 1% to 4% of the whole, and the balance mainly iron, said material having an initial permeability of not less than 250.

In testimony that we claim the forego-v 

